Chip-Scale Atomic Clocks (CSACs) and magnetometers both utilize vapor cells that enclose vapors of alkali metals—typically either rubidium (Rb) or cesium (Cs). A laser sends a signal at an optical wavelength through the vapor cell, exciting hyperfine transitions using a phenomenon called coherent population trapping (CPT). A cesium-based CSAC, for example, may use a laser that is tuned to the D1 absorption line of cesium at 894 nm. The laser sweeps a frequency region around the absorption line and monitors, at a photodetector, the amount of the light that is absorbed in passing through the vapor cell. The region of maximum absorption is detected and used to stabilize a reference frequency that is provided by the CSAC or magnetometer. The intrinsic noise in the system can hamper attempts to increase sensitivity in the measurements.
CSACs and magnetometers utilize similar structures, with one exception. With no external magnetic field, the Zeeman levels of an electronic transition are degenerate. However, in the presence of an external magnetic field, the degeneracy is broken, and the Zeeman levels are split in energy by the gyrometric ratio and the quantum number of degeneracy mf=0, +/−1, . . . +/−n. Structurally, this means that when the vapor cell is used for a CSAC, magnetic shielding is provided around the package to eliminate the external field and allow for a bias to provide a fixed splitting of the Zeeman levels; however, a magnetometer uses the spacing of the split absorption lines to measure the intensity of the magnetic field. Accordingly, different packages need to be produced to satisfy the needs of these different uses. Improvements to the fabrication and stability of these devices are desirable.